Invasive Species Management

Japanese beetle adult on leaf.

2023 Japanese Beetle Citizen Science Project

Landowners may enter their information to help us better understand the Japanese beetle populations along the Front Range.  

We will be using our online map to track early emergence and document the preferred Colorado hosts. 

Reporting Form

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Need Noxious Weed Advice?

  • For properties within unincorporated Jeffco - We are able to answer calls and questions. Our hours are Mon -Thur 6:30 am - 5 pm.  See our contact information on the right-hand side of this page.
  • For properties within city limits please contact your city's weed authority.

Weed of the Month

Each month we will feature a noxious weed to help landowners identify weeds they may encounter on their property.

Plumeless thistle

June 2023

Plumeless thistle (Carduus acanthoides) is a List B member of the Sunflower family (Asteraceae).  It is a biennial or sometimes a short-lived perennial.

Flowers are reddish-purple, ½-1 inch wide.  The bracts are narrow and tipped with a spine.  Flowers are present June to September and grow singly or in small groups at the tips of branched stems.

Plumeless thistle reproduces by seed.  The seeds lack a pappus.

Plants have taproots and can grow to 8 feet tall.  Stems are winged and branch towards the ends. Leaves are dark green with a lighter midrib.  The undersides of the leaves are hairy.

Rosettes form in the first year and bolt early in May to June of the next year.  The rosette leaves  are deeply lobed and spiney.

Plumeless thistle is found in disturbed areas, such as overgrazed pastures, rangelands, roadsides, and rights-of-way.

Originally from Eurasia, it has been known in the northeast US since 1837 and in Colorado since the mid-1950s.

MN Dept. of Agriculture

WASHINGTON STATE Noxious Weed Control Board

Photo Credits

Rosette - Loke T. Kok, Virginia Polytechnic Institute and State University,

Stem - Steven Katovich,

All others: Jeffco Invasive Species Management

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A Landowner's Guide - Developing a Noxious Weed Management Plan

We developed this guide to assist landowners.  The information provides steps to develop a management plan for properties that have noxious weeds.

Download your copy

yellow_flag_iris Weed Spotter

The Weed Spotter program is a citizen science based effort to detect 6 high priority species on Jeffco Open Space parks.  Learn more at our Citizen Science page.